A sealing ring that slides against a cylinder tube is attached to a piston that is accommodated in a fluid pressure cylinder so as to define an oil chamber within the fluid pressure cylinder. For this purpose, a ring-shaped accommodation groove that holds the sealing ring is formed in an outer periphery of the piston.
To attach the sealing ring to the piston, a diameter of the sealing ring is increased using an attachment jig, whereupon the sealing ring is guided into the accommodation groove along the outer periphery of the piston. Having reached a periphery of the accommodation groove, the diameter of the sealing ring is reduced using a correction jig, whereby the sealing ring is fitted into the accommodation groove.
Hence, the sealing ring is attached to the piston using a plurality of jigs, and therefore an increase in a number of steps required to assemble the piston is unavoidable.